1. Field of the Invention
The present invention relates to light-emitting diode (LED) control systems and methods, and more particularly to an LED control system that calibrates monochromatic LEDs according to monochromatic light beam feedback of the monochromatic LEDs.
2. Description of the Prior Art
At present, video displays incorporate light-emitting diodes (LED) as a light source of a backlight module. Using LEDs as the light source of the backlight module creates a problem of color shift, or deviation from white color. Color shift in the LEDs of the backlight module causes color shift in the video display. The problem with color shift is caused by difficulty in controlling the quality of the color range of light emitted by each LED to be at the same level. Perception of color by the human eye is an intricate process. In order to quantify the description of color, Commission Internationale de l'Eclairage (CIE, International Commission on Illumination) performed vision experiments to record the visual sensation of the eye of observers brought about by lights with different wavelengths, and deduced the CIE 1931 Color Matching Function for the colors red, green, and blue. According to this Color Matching Function, colors are quantified by chromaticity coordinates. Colors in a display are also expressed through chromaticity coordinates. As the human eye increasingly demands higher color quality, backlight modules with high luminescence and color quality are needed for use in displays.
For example, if LEDs of the three fundamental colors (RGB) are utilized as a light source of a backlight module, the brightness of the light outputted by LEDs changes with changes in temperature or prolonged periods of use. The change in brightness is not exactly the same for each LED with different color, such that the overall brightness of the light source is unstable, and the color coordinates thereof undergo a shift. To improve on this condition, U.S. Pat. Nos. 6,630,801, 6,894,442, 6,441,558, 6,127,783, 6,495,964, 6,510,995, 6,753,661, 6,552,495, 6,992,803, and 6,998,594 disclose utilization of a result of sensing the fundamental RGB light outputs of the RGB LEDs to perform closed feedback control to correct the problem of the unstable LED light source. Only the three fundamental color RGB sensor signals act as a feedback signal. There is no way to use the brightness of the light formed by the combination of the lights of the three fundamental colors RGB directly as the feedback signal. Namely, it is not possible to obtain the brightness value of the light outputted by the backlight module directly in the prior art. Instead, the brightness value of the outputted light of the backlight module must be calculated from the respective brightness values of light of the three fundamental colors RGB. Accordingly, the calibration method of the prior art cannot directly perform feedback control on the light source outputted by the backlight module, and thus cannot truly improve on the instability of the LED light source.